US1752330A - Suppression of interference in carrier telegraph systems - Google Patents

Description

Aprill, 1930. RR H. CLAPP 1,752,330

SUPPRESSION OF INTERFERENCE IN CARRIER TELEGRAPH SYSTEMS Filed Ndv, 15', 1928 I [Ii 0251143441100 Receivin Cucuz I INVENTOR ATTORNEY g signaling channel or' channels.

Patented Apr. 1, 1930 UNITED "STATES PATENT OFFICE I :BOBERT H. CLAYP, OF RAMSEY, NEW JERSEY, ASSIGNOB TO AMERICAN THEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK SUPPRESSION OF INTERFERENCE IN CARRIER TELEGRAPH SYSTEMS Application filed November 15, 1928. Serial No. 318,602.

produce, in response to the disturbance, an

impulse which tends to hold the armature of the receiving relay against the contact upon which it happens to rest at the instant of the disturbance. This holding impulse is caused to flow through awinding of the receiving, relay, and in order that it may always be in such a direction as to hold the relay armature on its contact, a reversing arrangement is provided for reversing the direction of flow of current through such winding as the signal changes frornmarking to spacing and vice versa.

The foregoing arrangementinvolves setting aside a frequency band for the buck circuit which cannot be used for signaling. Fur= thcrrnore, in order that the arrangement may be effective, the disturbance must occur simultaneously in the band assigned to the buck channel and the band or bands used for the I In accordance with the present invention, it is-proposed to overcome thesefilimitations byusing the same frequencyjband both for signals and for the neutralizing impulse. This is accomplished by associating with each receiving rectifier of the signaling channel an auxiliaryrectifier for producing, in response to a disturbance, a momentary impulse which will flow through a winding of the receiving relay in such direction as to oppose the effect of the disturbing impulse in the relay during spacing and to assist the rectified current suppliedby the receiving rectifier during marking. The proper poling oftherneutralizing impulse may be accomplished as in the buck signals corresponding to spacing. Experience shdws channel circuit by a suitable reversing arrangement. In order to prevent the auxiliary rectifier from responding to marking signals, its grid is biased sufiiciently ne tive so that its space current is substantialfi zero when normal marking signals are being receivedgf Withsuch an arrangement, 'no current will besupplied by the auxiliary rectifier during the reception of waves of normal carrier frequency amplitude corresponding to marking enduring the zero current interval that the interfering disturbances are, for the most part,'of much greater magnitude than the carrier current received during the marking interval. Consequently, when such-a dis turbance occurs it will cause current to flow in the auxiliary rectifier. This current is so poled by the reversing arran ,ihe'nt that it tends to hold the armature ofihe receiving relay upon either its marking or spacing contact depending u on the character of the signal ing receive" at the time of the disturbance. v

The invention will now be more, fully understood from the following description, when read in connection with the accompanying drawing, the figure of which illustrates circuit arrangeemnt embodying theprini i'tples of the invention.

In the drawing, the apparatus of a single carrier channel only is shown, it being under stood, however, that other similar channels may be provided in a multiplex system, either wire or wireless. The receiving channel comprises the usual selectin circuit S, which may be a tunedcircuit orja nd filter or other known device for selecting the band assigned to the particular channel A reoeivingamplifier A is also provided for amplifying-the received carrier waves, the plate circuit of this amplifier being supplied with current through the usual choke'coil L. The regular an operating winding 1 of the'receiving relay RR. The receiving relay also includes a biasing winding 3 through which a normal current flows of such magnitude as. to produce a pull upon the armature of the relay, tend ing to hold it against its spacing contact, this pull being about one-half as strong as that due to the rectified current flowing through the winding 1 iii response to a marking signal; Thus, during spacing signals when no current flows in the circuit of the rectifier D, the armature is held against the spacing contact, but when a train of carrier waves corresponding to a marking signal is re-' ceived, the rectified current flowing through the Winding 1 shifts the armature to the marking contact.

In order to overcome the effects of disturbing impulses, an auxiliary detector D is associated with the output of the amplifier A.

The grid is biased by means of a 0 battery CB which is connected between the grid and the filament through a resistance 1". This resistance is provided in order to. prevent the i low impedance of the grid battery from act ing as a shunt with respect to waves transmitted from thereceivingamplifier A. Such waves will be transmitted to the grid of the detector D through a capacity C which also serves to isolate the grid of the detector D from the potential of the plate battery of the amplifier A. The grid battery CB is so arranged as to render the grid of the rectifier D more negative than the grid of the rectifier CB, so that. no plate current will flow in the detector D until an applied wave is superimposed upon its grid with a magnitude greater than the normal carrier waves received during the marking impulse. 'Consequently, the detectorD produces no eifectduring the receipt of normal marking and spacing signals. As already stated, however, the disturbing waves are usually of greater amplitude than the normal signaling currents, and consequently, whenever such a disturbing wave is received, a current will flow in the plate circuit of the rectifier D, as will be described in more detail later. 'This plate current-flows through an auxiliary winding-of the receiving relay RR'in a direction-determined by the contacts of two polar reversing relays PR and PR. Thesereversing relays are cone necte'd in the loop circuit which is controlled by the receiving relay RR, and their arma cause the armatures of relays PR and PR to rest upon their lower contacts. If, with the circuit in this condition, an interfering disturbance should occur, such interfering wave, upon being impressed upon the grid of the detector D, will cause a plate current tofflow through the winding 1 of the receiving relay. Since the disturbing wave will usually be of much greater amplitude than a normal marking current, this impulse through the winding 1 will be sllflicicnt, under normal conditions, to shift the armature of the receiving relay to its marking contact. This action is prevented, however, by the fact that the disturbing wave is also applied to the grid of the detector D, and

being of large amplitude it overcomes the normal negative potential of thp grid D sufficiently 'to' cause a plate current to flow over the lower contact of the reversing relay PR through the winding 2 and thence over the lower contact of the reversing relay PR. This current through the winding 2 is in such a direction as to oppose the current through the winding 1. It will also be sufficient to prevent the current through the winding 1 from shifting the armature, because the disturbing impulse will usually be of sufl icient amplitude to overload the tube D and hence, the plate current of the tube D will not exceed its saturation value. Although a greater potential must be applied to the grid of the tube D in order tol iovercome 'its,norma1 bias, than need be applied to the grid of the tube D, the actual potential applied is so great in both cases that the plate current of the tube D will also be a saturation current and hence, as great as the plate current of the tube D. The effect of the disturbing impulse is therefore neutralized duringthe spacing condition. VVhen a marking signal is being received, carrier waves are impressed upon the grids of the rectifiers D and D". As already stated,

the grid of the detector D.- is biased sufficient ly negative so that under these condition; no space current flows in the plate of the detector D. In the case of the detector D, however,

which is biased negative to alesser degree, a rectified plate current flows through the winding 1 of the receiving relay RR and shifts the armatuneofthe receiving relay to its marking contact. The polar relays PR and PR in the loop circuit thereupon shift their armatures to their u per contacts so that the plate of the detector 1 is connected to the winding 2 of the receiving relay in such a manner as to cause current from the plate (when flowing) to flow through the Winding 2 in the opposite direction to that described in connection with the spacing impulse.

The effect of a disturbing impulse during marking is not always the same. In some instances the disturbing impulse appears to have the cfi ect of increasing the plate current in the rectifier D. This or course, has no at fect of producing fa se rfignal, and if a current is also caused. to flow in the plate circuit of the rectifier I) in It'xpullsQ to such a disturhance such plate run/em will assist the plate current from the rctifiei i to hold the armature against the marking contact until p the disturbance ceases. The H. .u arises in connection with disturl m new i a t ypc that they cause a decree in the p re current of the detector 1), tliei feet of producing a fals While the cause of this dc current is not fully understw i, ly due to the action of the r the capacity C as a grid leula The disturbing impulse may tail e a high frequency Wave within tte ass; tau selecting circuit S, the Wave ueia, great amplitude as to overcome ih -r negative bias of the grid of the det'ccit drive the grid positive so that eienrni from the filament to the grid. Div i negative clcmrons passing to the grit: c each positive hal f-Wave of the dist current magative charge is trapped up 4 grid Whit :1 quickly builds up, and by rend ing the id more negative tends to I'Htltl irar z-- ill. .7 r, :1 the amplitude of the disturb ivavc is net too great, so that the grid of it: rectifier Y (with its larger normal nega im bias} is actually driven positive durii iii-wave, a rectified current ill 2. plate circuit of the rectifier D in response U the disturbing impulse. This plate curres u may have a value equal to that, of the saturation condition of the tube, or th plate current may be smaller, depending upon the amplitude of the applied wave. In any event, the rectified current flows through the winding {tin such a direction to assist the late current;- of the rectifier D (it amp) and once, tends to pnavent the false spacing signal due to the reduction of the plate Cll'lffilll in the rectifier If the disturbing wave is of such amplitude as to actually drive the grid 01" the tulicl) positiveso that the grid draws current from the filament, thereby trapping a negative charge upon the grid due to the action of the condenser C and the resistance 1" acting as a i last i grid leak, the plate current of the rectifier D may be less than its maximum or saturation value. Such plate current, however, will be in such a direction as to tend to h. hi the armafew in number that the ouL; he Egwmi lt Wlll be obvious that tha w-ral pr s pics herein disclosed may many other organization: from those illustrated .thnt from the spirit of the in in let: us: deli the following claims.

\Vhat is claimed is:

1. In a carrier telegraph i can ii rcrewin; channel including a reel n g r52: t interns flu responsive to an intcrfciin; war: in said channel to produce cur: in1g'--"u and means controlled b5 the irir g via. to apply said current llaiplihh' t. w ll :vin as to tend to hold its urn a? against 83w if contict upon which it rm: u 2 im n: inu-rfcring Wave oer-um.

2. in a carrier telegraph w v ingf cha uel including a la.

us associated withsaid mi: 2 1 u naive to waves of now, i am l received in said chum-i I. c an ne rz ponsive to in rrl ez'in m'lhl mi-xl of great-ia npliiuh r ral 3 warn to producia an @135 1 means to app!" -np s t clayga'a as to ifl'i, fihilllt I J t t l pulse at. curpulse through said auxiliary winding when signaling carrier waves are not being received.

4. In a carrier telegraph system, a receiving channel including a receiving detector and a receiving relay, an auxiliary detector associated with said channel, said auxiliary detector being so biased as to be unresponsive to signal waves of normal amplitude received in said channel, but responsive to interfering waves of greater amplitude than normal signal waves to produce a current pulse, and means to apply said current impulse to said relay so as to tend to hold its armature against the contact upon which it rests at the time the interfering wave occurs.

5. In a carrier telegraph system, a receiving channel including a receiving detector and a receiving relay, an auxiliary detector comprising a vacuum tube having grid, filament and plate electrodes associated with said channel, said grid being so biased that no plate current will flow in response to normal signal waves but plate current will fiow in response to interfering waves of greater amplitude than normal signal waves, and means to apply said plate current to said relay so as to tend to hold its armature against the contact upon which it rests at the time the interfering wave occurs.

6. In a carrier telegraph system, a receiving channel including a receiving relay, said relay having an operating winding, an auxiliary winding, and means normally tending to bias the armature of said relay against one of its contacts, a receiving vacuum tube detector in said channel having its plate connected to supply operating current to said operating winding and its grid so biased that substantially no operating current will be supplied in the absence of received carrier waves, an auxiliary vacuum tube detector associated with said channel and having its grid so biased that no plate current will flow in response tonormal carrier signaling waves but plate current will flow in response to interfering waves of greater amplitude than normal carrier signai waves, and means to cause the plate current from said auxiliary detector to flow through said auxiliary winding in such direction as to assist said oper- 4 ating winding when carrier signal waves are vember, 1928.

being received and to reverse the direction of current flow through said auxiliary winding when carrier signal waves are not being received. V

In testimony whereof, I have signed my name to this specification this 14th day of No- ROBERT H. CLAPP.

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